Metal–organic framework-derived high conductivity Fe3C with porous carbon on graphene as advanced anode materials for aqueous battery-supercapacitor hybrid devices

Battery-supercapacitor hybrid (BSH) devices with aqueous electrolytes receive extensive attention due to their high potential. In this study, porous carbon coated Fe 3 C nanoparticles (C/Fe 3 C) are loaded onto reduced graphene oxide (rGO) nanosheets , forming rGO@C/Fe 3 C composite structure. The rGO@C/Fe 3 C composite is prepared by in-situ carbonization of rGO/Fe-MOFs. First-principles calculation proves that the high conductivity of the Fe 3 C mainly comes from d electrons of Fe and therefore can benefit the rate capability. The optimized electrode structure of rGO@C/Fe 3 C displays high capacity of 95.3 mAh g −1 at 1 A g −1 , enhanced rate performance (retaining 66.5% at 20 A g −1 ) and outstanding cycling stability (retaining 81.5% after 5000 cycles). Furthermore, a BSH device with Na 0.5 MnO 2 cathode and rGO@C/Fe 3 C anode structure shows an ultrahigh output voltage of 2.4 V in 1 M Na 2 SO 4 electrolyte, while its output voltage in 6 M KOH electrolyte is only 1.4 V. The observed energy densities of the device in two electrolytes are 46.2 Wh kg −1 at 1.2 kW kg −1 and 28.3 Wh kg −1 at 0.7 kW kg −1 , respectively. Therefore, the successful construction of the BSH device based on Fe 3 C/rGO provides an attractive strategy for the selection of anode materials .